132 THE ALGAE 



fairly well with those of Schussnig and Kothbauer. This worker 

 believes that in the Irish Sea the zoids from the unilocular spor- 

 angia probably do not fuse, as shown by Knight, but give rise 

 instead to haploid plants (cf Fig. 71). It would seem, therefore, that 

 the somewhat complex schema of these later workers is probably 

 the more correct, at any rate so far as the Neapolitan form is con- 

 cerned. In America the diploid plants were found growing epi- 

 phytically on Chorda or Spartina and these either bore pluri- or 

 unilocular sporangia independently, or else both could be found 

 on the same thallus. The unilocular sporangia occurred only in 

 summer, whilst the plurilocular were present throughout the whole 

 year. Although the zooids from both types of sporangia acted as 

 zoospores and germinated directly, nevertheless meiosis always 

 took place in the unilocular sporangia, the zooids of which de- 

 veloped into the sexual plants that were found growing as obligate 

 epiphytes on Chordaria, in some cases the nearest asexual plants 

 being twenty miles distant. It is suggested, therefore, that depend- 

 ence of the sexual generation upon a particular host may be rather 

 more common than is perhaps suspected. The plants growing on 

 Chordaria were dioecious and only bore plurilocular gametangia. 

 It must also be borne in mind that the variations in the life cycles 

 of the plants from these three locaHties may be due to genetic dif- 

 ferences because, although the chromosome numbers may be 

 identical, this would not exclude such a possibility. This extremely 

 large genus is now subdivided, and recently a number of new 

 genera have been established (Hamel, 1939). 



EcTOCARPACEAE : Pylaiella (after de la Pylaie, a French botanist). 

 Fig. 72 

 There are several species, one or two of which are widely dis- 

 tributed, e.g. P. {Bachelotia) fulvescens, P. littoralis, and although 

 the latter is said to possess quite a ntmiber of varieties it is by no 

 means certain that they may not be ecological or seasonal forms 

 because it has been shown that the movement of the water can even 

 affect the nature of the branches. In general appearance the plants 

 are very like Ectocarpus, and for many years the species was in- 

 cluded in that genus. The branching is opposite or alternate, but 

 the branches do not end in a mucilage hair as they do in Ectocarpus. 

 Attachment to the host plants or to the substrate is by means of 



